This proposal will continue to investigate the natural occurring canine distemper of chronic and "old dog encephalitis" (ODE) forms of encephalitis. Included will be studies to determine whether canine distemper virus (CDV) antigen is present in brains of dogs after recovery or after prolonged period following an attack of the acute central nervous system (CNS) disease. The investigation will include virologic methods to determine the state of the CDV antigen in the brain. Attempts to isolate competent virus and to detect defective CDV will be made. Specialized isolation techniques will be used for brains of dogs with ODE ad chronic encephalitis. Cell-mediated and humoral immune responsiveness of dogs with various forms of encephalitis and dogs that have recovered from acute CNS distemper infections will be examined. Immune competence will be tested by 2 methods: lymphocyte stimulation and macrophage migration-inhibition tests with CDV antigen. Humoral CDV antibodies, including CDV-specific complement-dependent cytotoxic antibodies, will be measured in sera and spinal fluid. The neurological manifestations of canine distemper encephalitis have been shown to be similar to acute measles encephalitis, SSPE and possibly MS in man. These studies on the canine distemper model are aimed to provide better understanding on the pathogenesis of virus-induced demyelinating encephalitis.